It is frequently necessary to form a connection to a pipe, tube or duct under pressure without cutting or discharging the pipe and without cutting off flow therethrough or materially reducing the pressure in the pipe.
For this purpose, tools have been developed which basically comprise a drill guide which can be attached to the pipe and include a lost fitting which is adapted to be sealed to the pipe around a hole to be drilled therein, a drill bit which can be displaced through the guide and which can be connected to a motor or the like for driving the drill bit and, of course, appropriate sealing means.
It is known, for example, to provide a drill guide or fitting which is to be attached with a valve, through the valve member of which the drill bit can be displaced and which can be then shifted into a closed position once the drill bit is retracted to close off the fitting without pressure loss in the pipe and allow the valve to be attached to a branch pipe or the like.
Tools of this nature are described in the French Certificate of Utility No. 2,210,741 and the French Certificate of Addition No. 2,283,382. Both of these tools permit drilling into a pipe conducting a gas or liquid under pressure without the need to vent or drain this pipe in the formation of a branch into the pipe.
In this arrangement, the casing for the drill is threaded directly onto the isolating valve. The valve is opened and the drill bit is caused to pass through this valve until it engages the pipe wall and drills through the latter. The drill bit is then retracted to permit closure of the valve and, as a consequence, the valve remains in place and serves as the connection to the branch conduit or pipe. Without loss of fluid and, of course, without voiding the interior of the pipe itself, therefore, it is possible to provide a branch to a line or pipe in use.
In several cases the drill bit may be of the coring-drill type or of the milling type which can have a central spur and which is able to cut a ring from the wall of the pipe to be pierced (see the French Certificate of Utility No. 2,210,741, U.S. Pat. Nos. 2,171,575 and 2,287,354 and British Pat. No. 1,368,751).
One advantage of this kind of tool is that the entire volume of the hole cut in the pipe is not converted into chips or debris. Nevertheless these tools are not able to eliminate all of the debris or even a significant amount of debris and thus the debris which is formed can stagnate in the region of the tee which has been premounted on the pipe and which can cause deterioration of elements which cannot be protected from the detrimental effects of such materials.
The drill bit can also be of the auger or helical flute type so that at least part of the debris is drawn away from the hole as it is made. This is the case in the French Certificate of Addition No. 2,283,382. This arrangement also does not solve completely the problem of eliminating chips and other debris forming during the drilling process.
Partial solution to the problem can be found in an analogous device described in German Pat. No. 322 665 where the drill bit is of the helical flute type and is able to eliminate the debris and chips at the pipe of the drill by causing the debris to collect in an annular chamber surrounding the tool. This chamber is located at the level of attachment of the drill structure to the tee or the fitting and is defined externally by a sleeve which surrounds the tool and which must, therefore be introduced together with the tool into the valve.
Obviously, because the chamber-defining sleeve must also be introduced through the valve and the cross section of the valve in its open position is limited, the size of the chip or debris-collecting chamber is likewise limited and the discharge of detritus from this chamber is difficult at best.
Furthermore, when the tool of prior art devices for the purposes described conforms to that of the drill bit of the helical flute type, the tool is either without protection as is the case with the tool of the French Certificate of Addition No. 2,283,382 or is protected only over a limited portion of its length as is the case with German Pat. No. 322 665 or poses a danger to the seals of the isolating valve.